1. Field of the Invention
This invention relates to linear bearings useful for enclosing a shaft or rod from which a sliding door is hung, for example, a door on a mass transit vehicle.
2. Description of Related Art
Current linear bearings used on door systems for rail vehicles have about 75N drag associated with them that creates friction requiring larger motors to move the doors to the open and closed positions. Typically, these linear bearings have many moving parts, for example, ball bearings that assist in translating the door along a rod or shaft mounted to the vehicle. Grease and other lubricants are used to keep these linear bearings running smoothly, although contamination is a problem causing failure, increased friction, and pitting of the rod or shaft. The linear bearings are generally enclosed in a bracket having a flat attachment plate for attaching the bracket to the vehicle door and a cylindrical housing for mounting the linear bearing. Typical linear bearings are expensive and costly to maintain in outdoor environments where large amounts of dust and other airborne contaminants are present.
The use of magnets to support at least a portion of the weight of structures, such as door hung from a rail, is disclosed for example in U.S. Pat. No. 4,698,876 entitled “Door Apparatus Partially Supported by a Magnetic Mechanism” and U.S. Pat. No. 7,013,605 entitled “Door Suspension Apparatus.” Typically, the magnets are not directly associated with the linear bearing that encloses the rail from which the structure is hung.